The present invention relates to a safety switch that has a bi-metal plate which has an end movably engaged with a gap defined in a switch member so that even if the switch member is stuck, the bi-metal plate is deformed when the switch is overridden.
A conventional see-saw switch is shown in FIG. 1 and includes a switch member 11 having a protrusion 110 which movably presses a plate 12 so that two contacts on two ends of the plate 12 can be respectively pushed to contact a corresponding contact point. This type of switch cannot automatically jump off when it is overridden. FIGS. 2A and 2B show a switch disclosed in U.S. Pat. No. 5,262,748 that includes a switch member 13 which has one end connected to a connection plate 14 which is connected to a bi-metal plate 170. A curve resilient plate 18 has one end connected to the easing 10 of the switch device and the other end connected to one end of the bi-metal plate 170. Three terminal plates 15, 16, 17 are connected to the casing 10 of the switch device and the bi-metal plate 170 has the other end thereof connected to the terminal plate 17. A contact point 171 is connected on the bi-metal plate 170 and another contact point 160 is connected to the terminal plate 16. The bi-metal plate 170 is lowered by pushing the switch member 13 to close the circuit. When the switch is overridden, the bi-metal plate 170 is deformed to separate the two contact points 171, 160. However, if the switch member 13 is stuck or if the resilient plate 18 fails, the bi-metal plate 170 will not be deformed. Besides, if the deformation force of the bi-metal plate 170 is larger than the force of the resilient plate 18, the resilient plate 18 will keep the bi-metal plate 170 at an open status. If the users push the switch member 13 again, the bi-metal plate 170 will jump off again, and this could result in sparks and has potential danger.
FIGS. 3A and 3B show a Taiwanese published patent No. 334165 that includes a switch 20 with a driving member 21 which is slidably engaged with a connection member 22. A spring 24 is connected between the driving member 21 and an inside of the casing of the switch device. A bi-metal plate 23 has one end thereof fixed to one of two terminal plates of the casing and the other end of the bi-metal plate 23 is engaged with the connection member 22. The bi-metal plate 23 contacts the other terminal plate when the switch member 20 is pushed. When current overrides, the bi-metal plate 23 is deformed and pushes the driving member 21 to let a convex portion of the driving member 21 engage with a recess 25 defined in an inside of the casing, and the bi-metal plate 23 is separated from the terminal plate. When either one of the switch member 20, the driving member 21 or the connection member 22 is out of order or stuck, the circuit cannot be opened. If the spring force 24 is too large, then the bi-metal plate 23 cannot jump off from the terminal plate, and if the spring force 24 is too small, then the bi-metal plate 23 could jump off often.
FIGS. 4A, 4B and 4C show a switch device disclosed in U.S. Pat. No. 5,760,672 that includes a switch member 28 which has one end connected to a connection plate 26 which has a hook portion for receiving an end of a bi-metal plate 27. Three terminal plates are connected to the casing of the switch device and a contact point 271 on the bi-metal plate 27 is to contact another contact point 272 on one of the terminal plates. A gap AS is defined in the hook portion so as to allow the bi-metal plate 27 to be deformed. However, this type of switch can only used with a specific type of see-saw switch member. Besides, because the switch member 28, the connection member 26 and the bi-metal plate 27 are normally engaged with each other, if any one of the parts is stuck or out of order, the bi-metal plate 27 could not jump off when the temperature drops, the deformed bi-metal plate 27 will contact the contact point 272 again. Because the overridden situation is not released, the circuit will be opened and closed repeatedly.
In accordance with one aspect of the present invention, there is provided a safety switch which comprises a casing having a first terminal plate and a second terminal plate. A first contact point is connected to the first terminal plate and a bi-metal plate is fixedly connected to the second terminal plate. A second contact point is connected to the bi-metal plate. A movable member is movably engaged with the casing and has two protrusions extending from an inside of the movable member. A free end of the bi-metal plate is movably located between the two protrusions.
The primary object of the present invention is to provide a safety switch device wherein the bi-metal plate is deformed even if the switch member is stuck.
The present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a preferred embodiment in accordance with the present invention.